Solar disinfection of fluid

ABSTRACT

A system for solar disinfection of fluid. One most preferred version of the system includes:
         (a) A UVTC, made of a polyethylene laminate film with an approximately rectangular plan, providing:
           a. A first compartment,   b. A second compartment for holding fluid, with a port to fill and dispense.   
           (b) A Disinfection Monitor Module (“DMM”) located in the first compartment which:
           a. Includes at least one sensor to measure light (e.g. solar UV) intensity   b. Provides at least one user interface including:   c. Contains a wireless communication interface   d. Operates according to a process that ensures sufficient cumulative exposure of the contained fluid to solar UV to achieve adequate solar disinfection.   
               

     Alternative embodiments may also include sensors to detect additional characteristics, such as transmittance, turbidity, “combined transmittance,” and/or temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/120,982 filed on Feb. 26,2015, entitled “System And Method For Solar Disinfection Of Fluid,” thedisclosure of which is hereby incorporated by reference for allpurposes.

TECHNICAL FIELD

The disclosed subject matter pertains generally to solar disinfection(“SODIS”), and more particularly, to a self-contained, portabledisinfection unit.

BACKGROUND INFORMATION

Ultraviolet (“UV”) light can be used as a means for disinfection. Inparticular, UV light from the sun can be used to disinfect fluids suchas water. The intensity of UV light, exposure time, temperature, andcloudiness of the water are important variables to determine the rate ofdisinfection.

SODIS is a procedure to disinfect contaminated fluid, typically drinkingwater, using solar radiation. Very generally stated, contaminated fluidis poured into a transparent container and exposed to the sun. Solarradiation, particularly UV radiation approximately in the wavelengths of320-400 nm (UV-A and UV-B), inactivates pathogens (e.g. bacteria,viruses, and other microorganisms) in the fluid; in the case of water,rendering the water safe for human consumption. The solar radiation alsoheats the contaminated water, and temperatures above 40 degrees Celsius(C) enhance this process. Further, if the water is maintained above acertain temperature for a sufficient period of time, e.g. 60 degrees C.for 1 hour, the heat kills pathogens and renders the water safe forhuman consumption (solar pasteurization). Studies have shown that theprocess by which solar radiation eliminates pathogens is acceleratedwhen the water is at higher temperatures. The presence of certainchemicals and compounds, such as photocatalysts (typically titaniumoxide), photosensitizers, and dissolved oxygen in the water will alsoaccelerate the SODIS process.

SODIS is advantageous over other forms of disinfection for a number ofreasons. Principally, the process is more economical than boiling orchemically treating contaminated water. In many areas lacking adequateaccess to potable water, fuel for boiling can be quite expensive andchemicals for treating water prohibitively so, if available at all.SODIS, by contrast, only requires an ultraviolet transparent container(“UVTC”) and readily-available solar radiation, preferably strongsunlight. Additionally, SODIS is more environmentally friendly thanother disinfection methods. Because the process uses only renewablesolar energy, water can be disinfected without the use of fuel andwithout requiring any consumable media, such as chemicals or replacementfilter media. Approximately five million people currently practice SODISusing polyethylene tetraphthalate (PET) beverage bottles.

Challenges with SODIS

Even though SODIS is conceptually simple, there are several practicalchallenges. These challenges generally reduce to knowing whether, when,and to what degree the process is underway and complete. Proper SODISrequires the right container, level of fluid cloudiness, and strength ofsolar radiation, which is a function of location and weather. Further,when faced with non-ideal conditions, such as cloud cover or weaksunlight, SODIS requires extended solar exposure and/or recognizing thatSODIS is infeasible with a given set of conditions. Some factors, suchas solar UV intensity, are unobservable with the naked eye. Further, itis impractical to manually measure and adjust for time-varying factorsrelated to weather.

Given the practical challenges of SODIS, a set of general guidelineshave been developed to increase the likelihood of conducting itcorrectly. It is typically recommended that water be exposed to directsunlight for six (6) to eight (8) hours in good conditions, whichinclude relatively clear water (<30 NTU, Nephelometric Turbidity Units),minimal cloud cover, and proximity to the equator. Contaminated waterleft outside for eight (8) hours during a period of moderate cloud covermay have received only a fraction of the radiation necessary to ensuredisinfection. Thus, a person consuming the water could still become sickdue to pathogens. In contrast, the disinfection process may move morequickly at high altitudes or nearer the equator where solar radiationdoses tend to be higher, so that water may be disinfected more quicklythan the time recommended by general guidelines.

In short, varying environmental and water quality factors can createuncertainty as to whether and to what degree the water has beenadequately disinfected by solar radiation. This uncertainty preventswidespread use of an otherwise economical and environmentally-friendlymethod of treating contaminated drinking water. Thus, a system andmethod that correctly determines and indicates when the SODIS process isunderway, to what degree SOIDS has progressed and whether it hascompleted, under a given set of conditions would greatly improve thedependability and consequently utility of the SODIS process. This wouldpromote greater use of the SODIS process and allow for increased accessto potable water.

SUMMARY OF THE INVENTION

Generally stated, the invention is directed to a solar disinfectionsystem. Embodiments include a system and method for determining whenSODIS is underway and to what degree SODIS is complete within a volumeof fluid. Embodiments implement a container having a first compartmentfor containing fluid and a second compartment for housing a DisinfectionMonitor Module (“DMM”). The container is configured such that inoperation the container defines a first surface substantially normal toa direction of radiation, and the container orients a sensor portion ofthe DMM such that it is also substantially normal to the direction ofradiation.

Various embodiments implement one or more additional sensors forenhancing the performance of the system, such as a temperature sensor.Still other embodiments implement one or more additional emitters, suchas optical emitters or RF emitters for communicating data external tothe system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a shows a typical SODIS device.

FIG. 2 is an embodiment of the entire novel disinfection system.

FIG. 3 is a preferred embodiment of the Disinfection Monitor Module(“DMM”).

FIG. 4 is a preferred process for disinfecting a fluid using thedisclosed embodiments.

FIG. 5 is a schematic for a preferred embodiment that may be included inthe disinfection system shown in FIG. 2.

FIG. 6 is an embodiment of the DMM with a turbidity/transmittancesensor.

FIG. 7 is another preferred embodiment of the disinfection system.

FIG. 8 is a sensor apparatus configured to measure one or more ofcombined transmittance, turbidity, and fluid presence.

FIG. 9 shows photographs of one embodiment of the preferred system andof one embodiment of the preferred DMM.

DETAILED DESCRIPTION OF EMBODIMENTS

Generally described, embodiments provide a solar disinfection systemthat measures factors, including at least UV intensity. One core systemincludes a UVTC and an attached Disinfection Monitor Module (“DMM”),wherein the DMM measures and/or estimates the UV intensity received bythe fluid within the UVTC. By way of outline, this disclosure will beginwith a brief glossary of terms, followed by a discussion of certainadvantages that the disclosed embodiments have over other SODIS designs.Finally, the disclosure will proceed with a detailed discussion of thosedisclosed embodiments.

Glossary of Terms

As used throughout this document, the following terms have the followingmeanings unless otherwise specified:

“Solar Disinfection” (SODIS): A process of exposing contaminated waterto sunlight, particularly the ultraviolet (UV) components, sufficientlyto render harmless pathogens (bacteria, viruses, cysts, and othermicroorganisms capable of causing sickness if ingested). SODIS ismediated by UV light interacting with molecules within the water andpathogens to cause several types of chemical reactions.

“Solar Pasteurization”: A process of exposing contaminated water tosunlight in order to heat it sufficiently to kill any pathogens viapasteurization, typically requiring a temperature at or aboveapproximately 60 C for approximately 1 hour.

“Disinfection Monitor Module” (DMM): A system for measuring solardisinfection.

“UV Transparent Container” (UVTC): A container which allows ultraviolet(UV) solar energy from the sun to pass through its surface and to acontaminated fluid within.

“Fluid”: A fluid, typically liquid water, which contains impurities,including viable pathogens, and requires disinfection in order to bepotable.

“Light”: Optical-wavelength radiation, including but not limited toultraviolet radiation from the sun.

“Transmittance”: The proportion of light passing unimpeded through asection of fluid or other material.

“Turbidity”: The ratio of light scattered at 90 degrees to the lighttransmitted through a small fluid sample volume.

“Combined transmittance”: The proportion of light generated by anemitter that is detected by a sensor some distance away and orientedtowards the emitter. Combined transmittance may differ fromtransmittance in that the light may take multiple indirect paths fromthe emitter to the sensor.

“Cut and weld”: A process for manufacturing plastic bags from one ormore layers of film laminate stock, in which the stock is first die-cutinto the correct shape, then positioned in a tool which applies pressureand heat (through conduction, ultrasound, radio-frequency, or the like),forming welds between the separate layers. The process can also weldflexible or rigid plastic components to and/or between the stock layers,including handles and fixtures with threaded openings.

Discoveries of the Inventors

The inventors have closely analyzed the SODIS techniques and literatureavailable and envisioned today, and have identified several advantagesof the disclosed embodiments over those techniques.

.A Environmental/Water Properties to Measure

Academic literature identifies several factors as important predictorsof the solar disinfection process, including UV intensity at differentwavelengths, temperature, and cloudiness of the water. Cloudiness can bequantified and measured in different ways, including as lighttransmittance at specific wavelength(s) through a specific volume ofwater, and as turbidity. Turbidity is defined (Nephelomteric, ISO 7027)as the intensity of light scattered at 90 degrees to the lighttransmitted straight through a sample, divided by the intensity oftransmitted light. Turbidity is frequently used as a predictor of poorSODIS performance in scientific studies. However, scientific studieshave also established that transmittance is in fact a better predictorof SODIS, because it is the absorption, not scattering, of light thatretards the SODIS process.

Recognizing that the preference is to understand the amount of lightthat is actually reaching points within the volume of water, disclosedis an innovative sensor apparatus that makes a measurement similar totransmittance but which is a better predictor of solar disinfection.This measurement is the relative transmittance between an emitter and asensor, co-axially oriented towards one another, and separated by somedistance. Thus, the light from the emitter reaching the sensor is thesum of the directly transmitted light (transmittance) and the scatteredlight which happens to also reach the sensor (related to, but not equalto, turbidity). The sum of directly and indirectly transmitted light maybe designated as the “combined transmittance.” Unlike other systems, thedisclosed sensor apparatus uses just one emitter and one sensor, and itsmeasured values provide a better prediction of SODIS.

The preferred embodiment provides a sensor apparatus design to betterestimate SODIS progress by measuring the “combined transmittance” oflight between two points in the fluid volume without restrictingtransmission to line-of-sight. This emulates the amount of sunlightpenetrating the same depth of water as the emitter-sensor separation inthe apparatus, as is described below.

.B Liquid Presence Detection

Ideally, the sensor apparatus should not mistake the absence of waterfor water with a low level of cloudiness, because this will lead toerroneous estimates of turbidity or combined transmittance. Thepreferred embodiment uses LEDs and photosensors having epoxy dome lenseswith refractive indices which make it possible to differentiate theabsence of water (or any fluid with a higher refractive index than air)from the presence of water with any level of cloudiness.

.C Temperature is not Critical

Elevated temperatures, particularly above about 40 C, are known toincrease the rate of SODIS. Further, uneven heating of a vessel used forSODIS causes thermal convection, which aids the process by exchangingwater in greater- and lesser-exposed locations within the volume,mitigating the effects of cloudiness. Uneven heating and circulationmake it difficult to predict the SODIS process based on temperaturemeasurement at a single point on the edge of a container, especiallywhen thermal dynamics are easily effected by the temperature andradiated heat absorbance of the surface on which a transparent containeris placed. Under no normally encountered temperatures is the SODISprocess slower than standard rates which are observed up to about 40 C;therefore, temperature is typically not expected to make SODISinfeasible.

.D Modeling Algorithm

The use of cumulative UV exposure as the predictor for SODIS progress issimpler than other models which incorporate temperature or turbidity,but sufficient and reliable when the turbidity of the water isrelatively low (e.g., less than about 30 Nephelometric Turbidity Units(NTU)). Finally, ignoring temperature also prevents false indication ofsuccessful disinfection if the fluid next to a temperature sensor issubstantially warmer than the temperature of much of the fluid in theUVTC.

To minimize cost while preserving simplicity and robustness to variableconditions, embodiments preferably measure solar UV intensity with asensor that is selective for wavelengths known to drive SODIS, and insome embodiments measures fluid transmittance over the longest distancepossible that does not require substantial mechanical features toaccommodate a longer distance.

Advantages of the Disclosed Embodiments

FIG. 1 depicts a simplified system diagram of one SODIS system thatillustrates deficiencies with existing technologies. The SODIS system101 consists of a transparent bottle 103, a control unit 105, aphotosensor 107, a display unit 109, a solar cell 111, and a resetbutton 113. The control unit 105 is screwed onto the threads of theopening of the transparent bottle 103 and sits at the top of the bottle103. The photosensor 107, display unit 109, and solar cell 111 areattached to the outer surface of the control unit 105. The system 101 ispowered by the solar cell 111 and uses the photosensor 107 to determinethe amount of UV radiation the water has been exposed to. Once thesystem has determined that a sufficient UV dose has been received, thedisplay unit 109 indicates to the user that the water is safe to drink.The system 101 is activated when the user screws the control unit 105onto the top of the bottle, or when the user presses the reset button113. The unit also includes a temperature sensor located in contact withthe internal volume of the bottle 103.

The inventors have recognized various problems with the typical portabledisinfection system shown in FIG. 1, many of which can result in thedevice erroneously indicating that the water has been disinfected,potentially exposing the user to waterborne pathogens (which could leadto illness).

.A Container

First, the container must be provided by the end-user, which results ina lack of control or accounting for the quality or size of thecontainer. Regarding quality, the container (since it is chosen by theend-user) could be dirty or opaque to UV radiation (e.g. high-densitypolyethylene) but possibly transparent to visible light (e.g.polycarbonate, or borosilicate glass with impurities). Even a containerthat normally permits the transmission of UV radiation may deteriorateover time such that it blocks most or all UV radiation. As to size, thecontainer could also be too large, such that some regions of the volumereceive too little UV exposure. Existing SODIS users are oftenimpoverished people and they are challenged to produce clean, clearbottles of the recommended material (e.g. PET, polyethylenetetraphthalate). If the bottles used are too small (e.g. 500 mL beveragebottles or smaller), then many are required in order to treat even amodest volume of water.

.B Cloudiness

Second, the SODIS system shown in FIG. 1 cannot control or account forthe cloudiness of the water, which can block UV radiation. If the wateris particularly cloudy, UV radiation will be absorbed near the surfaceand fail to reach the deeper water within. This problem is exacerbatedif the container is too large, such that the radiation has farther totravel to reach all of the contaminated water. A user of the systemshown in FIG. 1 is required to filter or otherwise clarify the fluidbefore the SODIS process or risk insufficient disinfection.

.C Sensor Orientation

Third, the location and orientation of an exterior photosensor, as shownin the system of FIG. 1, is not ideal because the photosensor 107 maynot receive the same amount of solar radiation as the contents of thebottle 103. As a consequence, the system may either under- orover-estimate solar intensity and thus disinfection rate.Under-estimation occurs if the sensor 107 is pointed away from the sun'spath in the sky. In this case, the sensor measures less light than isactually reaching the assembly when the incoming light is not alignedwith the orientation (115) of the sensor 107 and control unit 105.Sensor orientation 115 in turn is determined by the surface upon whichthe user places the control unit and bottle, and by the diameter of thebottle. The sensor has diminished sensitivity to light from directionsin which the sensor is not pointed, particularly directions orthogonalto the normal to the surface (123). Still, that light has efficacy onthe water in the bottle, but the system 101 will incorrectly record lessprogress in the SODIS process. In particular, two illustrative examplesof the surface orientation with a smaller bottle 119 and with a largerbottle 117 show that unless the housing width 121 of the control unit105 is equal to the diameter of the largest bottle, the sensororientation 115 will be substantially skewed from the ideal direction123 of normal to the surface. In simple terms, unless just the rightdiameter bottle is used, the sensor 107 will not point straight up, asis preferred, but instead be directed partially sideways andconsequently receive less sunlight.

Alternatively, the photosensor 107 and control unit 105 mayover-estimate the light reaching the contents of the bottle becauselight is measured outside the UVTC, and without some other compensatorymechanism for the unknown and variable UV transmittance of the UVTC.

.D User Error

Fourth, to the extent that the system shown in FIG. 1 uses auser-activated reset button (e.g. 113 on FIG. 1), it is susceptible touser error because it depends on manual activation of the system eachtime a new bottle of contaminated water is used. For example, thecontrol unit 105 could be transferred to a new bottle of contaminatedwater while it is still processing, so it would falsely indicate thatthe new water has been adequately irradiated if a manual reset 113 isnot activated. Alternatively, the user could fail to activate the systemwith the reset button 113, e.g. due to confusion about correct usage,and the system would fail to determine how much radiation the water hasreceived.

Accordingly, there is a need for a solar disinfection system thataccurately measures the amount of solar radiation that a contaminatedfluid has been exposed to even if the fluid is cloudy, without requiringcareful placement and orientation of a control unit, and mitigates therisk of incorrect use that could result in sickness.

Discussion of the Preferred Embodiments

Briefly described, the preferred embodiments are directed to a SODISsystem that includes a UVTC and a DMM. In the preferred embodiment, theUVTC and the DMM are arranged in such a way that a rate of disinfectioncan be measured accurately.

.A General Design

FIG. 2, viewed in conjunction with FIG. 9, shows one embodiment of adisinfection system. The system includes a substantially UV transparentbag (212) with fluid compartment (203) and separate disinfection monitorcompartment (202), and includes a fill port (204) at the top of the bagwith threaded lid (205) and spigot (206) for dispensing disinfectedwater. The UVTC of the preferred embodiment is a plastic bagmanufactured with a “cut and weld” process. The UVTC preferably includesan integrated DMM (201) encapsulated in the disinfection monitorcompartment (202) within the bag (212). Preferably, the disinfectionmonitor compartment (202) is sealed off from the main compartment (203).The bag (212) of the preferred embodiment holds approximately 10 L ofwater, and when placed on a substantially flat surface (e.g. the ground)it lies so that the DMM's front face (307 FIG. 3) is oriented upward,normal to the flat surface. This upward orientation of the DMM ispartially ensured by a relatively stiff flange (208), possiblyincorporating stiffening material in addition to the bag layers, weldedaround part of the perimeter of the bag (212) and by the rigidity of theencapsulation within compartment 202. The preferred orientation of theDMM allows the UV light sensor to receive as much as possible the samesunlight which also reaches the fluid bag generally.

The DMM (201) and fill port (204) are both located toward the top of thebag (212) to reduce the likelihood that they get dirty or bear theweight of the bag if it is rested against the ground or other surfaceduring use. Further, in case the bag (212) is placed with the spigot(206) overhanging a raised surface—such as may be the case wherechildren can dispense water near head-height—the DMM (201) is in anaccessible location for checking disinfection status via the indicators(301, 302 FIG. 3).

The bag material may be a plastic film which has appropriateUV-transmittance at the needed thickness, composed substantially ofpolyethylene in a laminate with other materials providing mechanical,thermal, and biological properties, including resistance to adhesion ofmicroorganisms. The bag (212) has a generally pillow-like shape whenfilled, as shown in the cross-sectional view (250). The bag (212) may beassembled using multiple pieces of film joined with welded seams (210)and in addition to transparent film includes reinforced stiffeningmaterial (208), made preferably of plastic or the like along some edges.Welding, including thermal, radio-frequency (RF), or ultrasonic methods,is one cost-effective method of joining plastic film laminates for a baglike this.

.B Bag Shape

FIG. 2 shows the unique shape of the preferred embodiment of the UVTC.

The preferred embodiment, and others, cause the filled bag to have across-sectional depth of less than about about 10 cm, while providing aninternal volume near 10 L, and having a shape suggestive of a beveragebottle due to the welded partition creating the compartment for thedisinfection monitor. The bag plan of the preferred embodiment is arectangle with one truncated corner that creates a shape suggesting alarge bottle. It can further suggest a jug depending on handle placementat the truncated corner and placement of the fill port.

.C Carry Handles

Two mechanisms for carrying the unit are envisioned: a carry handle(207) comprising a die-cut slot with rounded ends in the reinforcedmaterial; or a carry strap (209) composed of the same material butextending beyond the bag edges. Ideally, the unit includes bothmechanisms as shown. However, alternative embodiments may include eithermechanism or other carry mechanisms not shown. The carry handle (207)allows the unit to be safely carried or suspended, e.g. while dispensingwater, with the fingers of one hand inserted in the opening, while thecarry strap (209) allows it to be carried hands-free over longerdistances by, e.g., wearing the strap over one's shoulder.

.D DMM Construction

Turning briefly to FIG. 3, shown is an embodiment of the disinfectionmonitor module (DMM) (201). The preferred DMM is constructed of a2-piece plastic housing enclosing a printed circuit assembly and twobutton plungers. Because the DMM (201) is sealed and securely entrappedin its compartment (202), the housing pieces can be preferably joinedwith snap-lock mechanical features or even friction fit. Many othertechniques may be used to join the two pieces, such as RF or ultrasonicwelding, with fasteners including screws, or the like. These are but afew examples of the unlimited ways the DMM housing may be constructed.

Five openings are preferably provided in the housing for the buttons(303, 304), visual indicators (301, 302), and light sensor (305)preferably co-located with a wireless emitter interface (306) in apreferably recessed area of the housing to maximize the range ofdirections from which light can reach both. As illustrated, theseopenings preferably face directly to the front of the DMM (201). Inother embodiments the indicators (301, 302) may be exposed throughopenings at the corner between the left and front faces of the DMMhousing, making them visible from the front side of the bag (212) if theentire system rests on an elevated surface near head-height. Otherorientations may also be employed and function equally well.

.E DMM Entrapment Benefits

Returning to FIG. 2, the monitor compartment (202) providesenvironmental protection for the DMM (201). As a result, the DMM (201)need not be impervious to fluid or dirt, reducing its cost andcomplexity. The entrapment of the DMM (201) within a compartment (202)of the bag material means that incoming light that reaches the DMM (201)will attenuate at the same rate as incoming light that reaches the fluidwithin the fluid compartment (203). For this reason, the intensitymeasured by the sensor (305) is substantially the same as the intensityat the inner surface of the fluid compartment (203). This featureenables the unit to automatically compensate for damage and changes tothe transmittance of the bag material over time, ensuring that the UVactually reaching the water is measured, and solving the problem ofunknown UVTC properties.

As an alternative to the monitor compartment (202), the DMM may insteadbe configured for attachment to the bag (212) and a portion of the bagmaterial (or similar material) may be laid over the DMM (201) tosimulate or approximate being within a compartment of the bag (212).Those skilled in the art will appreciate that many alternativeembodiments are possible that provide the disclosed benefit ofencapsulating or treating the DMM (201) with the same material as thebag (212) such that light reaching the DMM (201) will be ofsubstantially the same intensity as light reaching fluid within thefluid compartment (203).

.F DMM Temperature Sensor

The DMM (201) may, optionally, contain an internal temperature sensor.However, the physical separation of the DMM from the fluid compartment(203) means that the temperature measured this way may not stronglycorrelate with the fluid temperature. Nonetheless, as noted above,temperature is not a critical component of SODIS. Accordingly, theability or inability to detect temperature is not viewed as having asignificant impact on the efficacy of the preferred embodiment.

.G Bag Shape Benefits

The shape of the bag (212) (i.e. plan geometry as viewed from the front)without fluid inside of it allows it to lie flat and be stacked. Thishelps reduce the space necessary to ship the product in a shippingcontainer, thereby reducing the delivered cost. That the fluidcompartment (203) plan geometry is substantially a truncated rectanglerather than a square limits the maximum thickness of the filled bag inthe front-to-back direction. The maximum thickness is substantiallydetermined by the width of the fluid compartment (203) along its bottomedge. This is helpful to ensure that sunlight shining on the frontreaches the back, even when the fluid is cloudy. As a trade-off, thelowest cost design to increase usable volume for a given material areawould be a more circular plan, favoring a square or regular polygon withmore edges.

.H DMM Orientation

The bag (212) has stiffening members—in the preferred embodiment,plastic film stiffened by addition of stiffening layers, or by virtue ofwelding together the layers comprising the front and back—added alongits longer edges, causing the otherwise very flexible DMM compartment(202) and seam (211) joining it to the bag (212) to tend to rest at asimilar orientation as the long edge of the bag (212).

The preferred embodiment employs a weldable plastic film for thestiffening material (208) but other materials could be used with moreinvolved joining requirements, such as metal, plastic, or compositestruts, or specially designed fluid compartments which stiffen underfluid pressure. Thus, in some embodiments, the stiffening material couldbe a semi or fully rigid element.

The stiffening material (208) helps ensure that the DMM (201) remainsoriented in the plane of the bag (212) when it is placed on anapproximately flat surface (i.e. front of bag and front of DMM (307) areboth oriented normal to the surface). The stiffening material helpsprevent the DMM compartment (202) from drooping due to folding along thepartitioning seam (211), mitigating the problem of the light sensor(305) facing away from the sun's path, which would otherwise result inunder-estimation of the UV intensity. This solves the problem of poorsensor orientation (115) suffered by other technologies.

The perimeter of the bag may compress when the bag (212) is filled withfluid in order to accommodate the bulging (front-to-back) of the filledfluid compartment (203). This makes the perimeter welds wrinkle in a waythat is difficult to predict or control, potentially deforming the DMMcompartment (202) if the stiffening member was absent. If a rigid objectis welded into the perimeter, e.g., near the sensor module flap, thenthe perimeter cannot change in this local region and this problem willnot happen.

.I DMM Functional Internals

FIG. 5 is a schematic view of a preferred DMM, comprising centralprocessing unit (CPU) 502, power source 501, memory 503, sensingelements 504, 505, 506 and 507, and interface elements 508, 509 and 510.The power source 501 may include a disposable or reusable storageelement (e.g. disposable battery, rechargeable battery, capacitor) aswell as a generation component (e.g. photovoltaic, thermo-electricgenerator), or even a connection to an external power supply (e.g. ACmains power). Preferably, the power source is a coin-cell disposablebattery.

The memory 503 may include volatile memory, nonvolatile memory, or both.The sensors may include a temperature sensor 504, optical sensor ofradiation intensity 505 (preferably a photodiode), and eithercommercially-available fluid and turbidity and/or transmittance sensors506 and 507, or specialized sensor assemblies as described in thisdisclosure. The interface elements include a wireless device 508 thatmay provide optical (e.g., infrared, or the like), acoustic, or radiofrequency (RF) communication (e.g, Bluetooth, WiFi, NFC, and the like)with external systems, and in some embodiments may be a simple andlow-cost element such as an antenna or an LED.

Visual/audible indicators 509, preferably “wait” (301) and “safe” (302),allow the system to communicate status information, including estimateddisinfection status, to a user. The buttons/switches 510, preferably“start” (303) and “stop” (304), allow the user to initiate and controlthe operation of the system. In some embodiments, the indicators (509)may provide a bar chart-type representation of incremental process,including a representation of logarithmic (rather than linear) totalpathogen die-off. In some embodiments the buttons/switches and indicatorelements are replaced with a single element providing user input andoutput, such as a commercially-available LCD or similar touchscreendisplay. In some embodiments, status information including process (400)state and disinfection progress may be transmitted via the wirelesscommunication device (508) instead of or in addition wireless to via thevisual/audible indicators (509).

Operation of the Preferred Embodiment

To operate, the user removes the threaded fill cap (205) and fills thebag (212) with contaminated fluid, replaces the fill cap, then pressesthe start button (303), initiating a process substantially similar tothat illustrated in FIG. 4 and described below. The process isimplemented in the form of a disinfection program stored in memory (503)and executing on CPU (502) of the DMM (201). The disinfection programpreferably employs an algorithm that calculates the cumulative UV lightexposure and compares it to a threshold value determined viacalibration. Calibration entails experimentally determining acorrelation between percentage die-off of a particular representativepathogen and cumulative UV intensity measurements.

Preferably, the “wait” LED (301) blinks to indicate that thedisinfection program is estimating the intensity of solar UV measured bythe sensor (305) and read by the CPU (502). When the cumulative UVexposure of the bag (212) reaches a pre-determined threshold, the “wait”LED (301) stops blinking and the green “safe” LED (302) begins blinking.Preferably, if a pre-determined amount of time, such as 48 hours,elapses since the start button was pressed and the cumulative UVexposure does not reach the threshold, the system returns to a standbystate (402) and stops blinking the “wait” LED (301). This is expected tooccur if insufficient sunlight is available for a sustained period oftime, or if the user fails to locate the system in a sunny location,which means that the SODIS process has failed. The time limit is a safeguard because the effects of the disinfection process cannot be assumedto persist with a cumulative effect if significant time periods ofdarkness interrupt the UV exposure; academic literature recommends amaximum of a 2-day process, allowing one night of darkness to interruptthe UV dosing period.

In an alternative embodiment, the algorithm may apply the cumulativethreshold criteria to UV measurements recorded over the past e.g. 48hours; if a threshold is exceeded, then the program transitions to the“safe” state (408); if instead a minimum threshold is not met and atleast 48 hours have elapsed, the program returns to a standby state(402). This moving window approach allow successful completion of adisinfection cycle in circumstances of unreliable sunlight, e.g. in thecase that after the user presses the start button, one day of lowsunlight is followed by two days of half the required threshold amounteach. The alternative embodiment prevents the user having to reset theprocess at the beginning of the second day to avoid the time limit, adecision that would require guessing the amount of UV received so farand expected on the second day.

.A Usage Tracking and Wireless Data Retrieval

The disinfection system records its own usage, preferably including thecount and outcome of iterations of the disinfection process (400), ofbutton (301, 302) presses, and of measured solar UV intensity. Thisinformation can be retrieved using a low-cost wireless communicationinterface (508, 306) which transmits data to a compatible receiverdevice, preferably a smartphone having Internet connectivity and GPScapability. The communication mode is preferably modulated infrared (IR)light, but may be visible light, using a common protocol preferably fromthe infrared data association (IrDA) industry standard. The DMM (201)preferably transmits data via the wireless interface (508) when eitherbuttons (303,304) are pressed on the DMM, momentarily interrupting thenormal process (400) to retrieve variables from memory (503) which areupdated each time the process (400) changes state.

If visible light is used, a separate wireless emitter interface (306)may be eliminated and substituted with one of the user interface LEDs(301, 302), so that the device has no additional component cost toprovide this feature. The preferably Internet-connected compatiblereceiver device may then record its own location (e.g., using GPS, orthe like), and transmits the data and location coordinates to a databaseon the Internet for storage and analysis. If Internet connectivity isnot available, the receiver device stores the data and transmits it tothe database the next time it establishes an Internet connection.

Infrared (“IR”) communication is widely used in consumer electronicproducts, such as remote controls for appliances, and so the electroniccomponents mediating it are commercially available in assembliesspecialized for that purpose. In this case the interface (508) ispreferably an infrared (IR) LED (306). Compared to other modes ofwireless communication, IR involves less engineering cost and materialand component cost to design and manufacture. Other embodiments may useWi-Fi, Satellite, cellular data, Bluetooth, ANT, or similar radiofrequency (RF). In such an embodiment, the microcontroller in the devicemay be a Bluetooth or ANT chipset to minimize cost. In that case, thesmartphone to which the data is first downloaded can be one withbuilt-in Bluetooth or ANT capabilities.

Recording and making available for retrieval of this data is helpfulbecause embodiments are often used as an aid item distributed free ofcharge to end users, and the purchasing organization is concerned withensuring maximum and correct utilization of the product afterdistribution. The availability of detailed usage data is helpfulfeedback to enable program evaluation and iterative improvement ofdistribution and usage training procedures.

Some embodiments include measurement of optical properties of the fluidbeing disinfected. Measurement of transmittance, or “combinedtransmittance”, are preferable to turbidity for the reasons outlinedabove. Measuring transmittance is beneficial because the estimate ofdisinfection rate can be improved by accounting for attenuation of theincident sunlight within the water. In simple terms, these embodimentsmeasure the cloudiness of the water and model its effect on disinfectionby e.g. calculating the average amount of light reaching each part ofthe water volume. This calculated amount will be substantially less thanthe incident light at the surface of the bag if the water issubstantially cloudy (turbid), and knowing it allows the DMM to extenddisinfection times appropriately rather than depend on a threshold ruleignoring turbidity and requiring users to avoid water greater than, forexample, 30 NTU.

A measurement capturing cloudiness, including turbidity or combinedtransmittance value, is preferably integrated into the disinfectionalgorithm by scaling the estimated UV light intensity by a function ofthe cloudiness measurement value. This function is preferably linear,comprising a single coefficient determined by calibration experiments,but may be nonlinear.

.B Measurement of Combined Transmittance

FIG. 8 shows a schematic of an embodiment of an optical sensor apparatusthat can measure a fluid's combined transmittance, or turbidity, anddetect the presence of air (or any other gas with refractive index near1.0). The optical sensor preferably may be included as a feature of theDMM shown in FIG. 6.

In one embodiment, measurement of combined transmittance is accomplishedusing an emitter (805) radiating light into the container's water volume(808, contiguous with 203). A direct sensor (806) is preferably situatedto point directly at the emitter (805) across a short distance, orientedsuch that the emitted light (e.g., 803, 804) elicits a substantiallymaximal signal in the sensor (806). The emitter (805) is preferably acommercially-available LED packaged in an epoxy dome lens (801) andaffixed to a rigid support (802), preferably the DMM protrusion (602),which ensures a specific separation distance (811) and relativeorientation of emitter and sensor axes and sensors (806, 807). Thesensors (806, 807) are preferably photodiodes with similar integratedlenses, and may include pre-amplifier or functionally equivalentcircuits. Selective measurement of only light from the emitter, asopposed to ambient or direct sunlight, is accomplished by modulating theemitter output and measuring only changes to the modulated component ofthe receiver signal. A scatter sensor (807) may be oriented orthogonallyto the line-of-sight between the emitter (805) and the direct sensor(806), such that it best responds to radiation scattered at a 90 degreeangle to the original path of the light from the emitter (805).

The emitted light from emitter (805) follows a different radiationpattern depending on the refractive index of the fluid in theintervening space (808) following basic principles of optics. Inparticular, the apparatus geometry and lenses are chosen such that achange in the fluid from a lower to a higher refractive index—such asfrom air to water—causes increased dispersion in the radiation patternfrom the emitter (805). For example, if rays of light follow one path(804) in the presence of air, they may follow a different path (803) inthe presence of water, and consequently not be detected by direct sensor(806), decreasing the combined transmittance measured by the sensorapparatus. This enables the detection of fluid presence, because airwill cause a higher combined transmittance measurement than can possiblybe achieved with pure water. Any combined transmittance measurementlower than that of pure water is preferably attributable to cloudinessof the water, under the assumption that the fluid is either water orsubstantially pure air. Therefore, the single transmittance measurementfrom this sensor apparatus (800) can both differentiate air from waterand also measure the combined transmittance.

Measuring combined transmittance over a relatively longer distance ispreferred because the attenuation of light over the longer distance isgreater, increasing sensitivity, and because this creates increasedopportunities for scattered light from the emitter (801) to reach thesensor (806), emulating the process of solar UV arriving at locations atgreater depths in the water volume via direct transmission as well asscattering.

Other embodiments of the sensor apparatus (800) may provide angles otherthan 90 degrees and 0 degrees between the emitter (801) and sensor (806)orientations. Still other embodiments may include only one sensor (806)but may also include multiple sensors.

.C DMM Embodiment with Sensor Apparatus

Returning to FIG. 6, shown are the physical features of one embodimentof a DMM housing (600). These physical features enable the housing toprotrude into the fluid compartment (203) of the UVTC bag (212) andfurther to locate light emitter (805) and sensor elements (806, 807) toenable measurement of transmittance, turbidity, and detection of fluidpresence via refractive index. This embodiment additionally includesmechanical features (610) to block the direct transmission of light fromthe emitter to the sensor oriented orthogonally to the emitter axis, inorder to measure only light which is scattered onto that sensor. Toreduce sensor signals caused by light other than that from the emitter(805), such as light from the sun, the housing may preferably includeshrouds or counter-sinks (608) to block such interference with intendedoperation.

.D Temperature Sensor

DMM embodiment (600) may optionally include a temperature sensorpreferably located in or at the surface of the protrusion (602) tomaximize its thermal contact with the fluid compartment (203). Thisallows the algorithm for determining SODIS progress to optionallyinclude water temperature.

Alternative Embodiments

.A Apparatus

FIG. 7 shows an alternative embodiment in which the sensor apparatus(800) is included by incorporating a protrusion (602) of the DMM housing(600) from the DMM compartment (202) into the water volume within fluidcompartment (203), across the partitioning welded seam (211), whichlocates the sensor apparatus (800) within the water volume of the fluidcompartment (203).

Also shown in FIG. 7 are additional aspects of alternative embodiments.Access to the DMM (600) for maintenance, replacement, or batteryreplacement, may be provided by an opening in the monitor compartment(202), such as a low-cost re-sealable zipper closure (702) which isfurther secured by a welded seam (706), such that cutting along aspecific path (704) bypasses the seam (706) and grants access to thecompartment (202) via the re-sealable closure (702).

One or more baffles (708) in the bag (212), comprising a weld within thefluid compartment (203) or a piece of film welded between the front andrear bag surfaces with the same weld plan, allow the bag (212) to have agreater internal volume if its dimensions are increased, while stilllimiting the maximum front-to-rear thickness of the filled bag. One ormore grommets (710) or similar reinforced openings in the stiffeningmaterial (208) or welded seams (210) allow embodiments to be hung, suchas on a nail, post, or rope for conveniently dispensing water.

.B Process

FIG. 4 is an illustrative process (method 400) for performing solardisinfection in accordance with the preferred embodiment. At 402, method400 includes maintaining a device in standby mode. At 404, method 400includes receiving an indication from a user. The user preferably maydepress the “start” button (303) as an indication to prompt method (400)to advance to the next step, preferably SODIS update (412), skippingstates (406, 408). However in some embodiments, the process may start byadvancing to measuring transmittance. In still other embodiments, themethod 400 may start by automatically advancing from standby (402) tomeasuring transmittance (406). Some embodiments advance to SODIS (412)only if the transmittance is within a prescribed range, precludingoperation if it is too low (insufficient UV reaching the water) or toohigh (indicative of air rather than water between the emitter (805) andsensor (806)).

At 406, method 400 includes measuring transmittance of a fluid, but insome embodiments this includes measurement of combined transmittanceand/or turbidity. At 408, method 400 determines if the transmittance isacceptable. If it is not, at 410 method 400 includes displaying an errorto the user and returns the device to standby mode at 402. If it is, thesystem begins estimation of the SODIS process at 412 by measuring one ormore of UV, temperature, and updating SODIS programs.

The SODIS process may estimate other environmental and fluid conditionsbefore execution of methods for estimating a disinfection status. At414, method 400 includes determining if a disinfection statuscalculation has been interrupted. For example, the disinfection statuscalculation may be interrupted by the user pushing the stop button(304). Further, the disinfection status calculation may be interruptedby environmental, fluid, and/or time conditions if such conditions falloutside a specified range, including combined transmittance. If aninterruption or unacceptable condition occurs at 414, method 400 returnsto the standby state at 402. If NO, method 400 includes determining ifthe SODIS is complete at 416. If YES, at 418 method 400 includesdisplaying an indication to the user that the fluid is safe to drink.

In this way, the system transitions from a calculative state to a safestate in which it indicates to the user that the fluid is disinfected,preferably by blinking the “safe” indicator 302. At 420, method 400includes determining if the user provides a command, preferably pressingthe “stop” button 304. If NO, method 400 includes continuing to displaythat the fluid is safe to drink. If YES, method 400 may restart andtrigger a return to standby at 402. It should be appreciated that method400 is provided as an example and may include additional steps. Further,method 400 may be completed by omitting one or more steps. Furtherstill, it shall be appreciated that the particular order of method 400as shown in FIG. 4 may be configured in another order in otherembodiments. This process flow represents a simplified description ofone embodiment only.

.C Detection of Container Opening

To prevent accidental or intentional incorrect use of the device (e.g.changing the water in the unit without resetting, creating theappearance of treated water) in some embodiments, a sensor (406) detectswhether the screw cap (205) or equivalent inflow/outflow port is opened.The sensor may be a simple mechanical switch depressed by the screw cap(205) moving into closed position. In the process (400), the port sensordetecting a closed state replaces indication from a user (404), anddetection of an open state replaces stop (420) and user-triggeredinterruption (414). In other embodiments, the process (400) can refuseto enter the in-progress state (412) until the port is in a closedstate.

.D Auto-Start

Some embodiments have a different method of initiating and stoppingprocess (400). Rather than require a user to press the start and stopbuttons, implicitly informing the disinfection monitor of when untreatedwater is present in the bag, these alternative embodiments automaticallybegin the disinfection process when water is detected by the combinedtransmittance sensor, and automatically return to the standby state whenair is detected. This is implemented in process 400 by skipping state404 and using high transmittance (indicating air detection) as aninterruption condition in state 414. If air is detected for only a shorttime duration, the process may preferably continue, allowing thepossibility that an air bubble came in contact with the combinedtransmittance sensor.

These embodiments address the problem that the user is depended upon totell the system when to start the disinfection process, and mayintentionally or unintentionally replace treated water with untreatedwater whilst the disinfection monitor continues to indicate “safe”status.

A variation on the automatically starting and stopping embodiments is topreserve at least a button-triggered stop condition (420) to return tostandby (402) so that the user can reduce the power used by the systemwhen “safe” indication (418) is no longer necessary, and also enjoygreater manual control over the system's operation.

The welded seam 211 is included as a consequence of the cut-and-weldmanufacturing process and may be substituted with elements similarlyproviding structural reinforcement, attachment of different materials,and partitioning of compartments, in other embodiments. The threadedport 204 and spigot 206 may be substituted with other elements providinga re-closeable fill and dispensing port, including separation of thefill port and dispense port, in other embodiments.

Specific Implementation of Preferred Embodiment

FIG. 9 includes photographs of one embodiment in which the DMM (201)measures only UV intensity, and the UVTC is a bag with reinforcingmaterial (208) affixed along the long edges of the bag and continuing ina loop to form a strap (209) for carrying the system. The DMM (201) isalso shown in a separate photo, removed from its compartment (202).

CONCLUSION

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to othertypes of fluids; thus, it is to be appreciated that the technology isnot limited to the disinfection of water. Further, the above technologycan be applied to other sources of UV light and is not limited to UVlight from the sun. The subject matter of the present disclosureincludes all novel and non-obvious combinations and sub-combinations ofthe various systems and configurations, and other features, functions,and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

Other embodiments may include combinations and sub-combinations offeatures described above or shown in the several figures, including forexample, embodiments that are equivalent to providing or applying afeature in a different order than in a described embodiment, extractingan individual feature from one embodiment and inserting such featureinto another embodiment; removing one or more features from anembodiment; or both removing one or more features from an embodiment andadding one or more features extracted from one or more otherembodiments, while providing the advantages of the features incorporatedin such combinations and sub-combinations. As used in this paragraph,“feature” or “features” can refer to structures and/or functions of anapparatus, article of manufacture or system, and/or the steps, acts, ormodalities of a method.

In the foregoing description, numerous details have been set forth inorder to provide a sufficient understanding of the describedembodiments. In other instances, well-known features have been omittedor simplified to not unnecessarily obscure the description. A personskilled in the art in view of this description will be able to practicethe disclosed invention. The specific embodiments disclosed andillustrated herein are not to be considered in a limiting sense. Indeed,it should be readily apparent to those skilled in the art that what isdescribed herein may be modified in numerous ways. Such ways can includeequivalents to what is described herein. In addition, the invention maybe practiced in combination with other systems. The following claimsdefine certain combinations and subcombinations of elements, features,steps, and/or functions, which are regarded as novel and non-obvious.Additional claims for other combinations and subcombinations may bepresented in this or a related document.

What is claimed is:
 1. A method for photochemical treatment of a fluid,comprising: initiating a process monitoring activity in response toeither a user signal or an auto-start condition, estimating solardisinfection of water in a container, the container being substantiallytransparent in at least one area, the estimating comprising: measuringlight intensity with a sensor module integrated into and calibrated foruse with the container, and supplying the measurements to an estimationalgorithm derived from models of the photochemical treatment process;indicating process completion, or degree of completion, based onspecific criteria for the process state estimated by the algorithm; andreturning to a standby or reset state upon either a user signal or inresponse to an auto-stop condition.
 2. The method recited in claim 1,wherein the algorithm integrates the measured light intensity over timeto generate a cumulative exposure value, and indicates processcompletion, or incremental progress, when this value exceeds one or morethreshold values comprising the calibration values for the device. 3.The method recited in claim 1, wherein the estimating step furthercomprises measuring temperature, fluid optical properties, or otherproperties of the fluid.
 4. The method recited in claim 1, wherein thelight intensity is measured at wavelengths impacting solar disinfectionof water.
 5. The method recited in claim 1, wherein the light intensityis measured at either UV-A wavelengths, UV-B wavelengths, or both UV-Aand UV-B wavelengths.